Most photographers buying a lens will look first at the offerings that the camera maker has, Canon lenses for a Canon Camera. Then they will buy what they can afford. This Sigma 35mm f1.4 DG HSM A would make this a very bad strategy.
With higher sharpness, lower distortion, better transmission and lower chromatic aberration than its main rivals. Only in vignetting does it fail to excel, having a 2 stop fall off in the corners when used at full aperture, though this is also true of the others. It is not just in the sharpness scores where the Sigma excels: the DxO Mark scores place the Sigma at just over 30, the f2 Carl Zeiss lens at 27 and the Samyang f1.4 lenses at 26 and 23 respectively.
From a price perspective the Sigma is the second cheapest of this group, about 50% more than the Samyang 35mm f1.4 AS UMC. However, the Samyang, like the more expensive Carl Zeiss Distagon T 35mm f2 and the much more expensive Carl Zeiss Distagon T 35mm F1.4 ZE lens is not fitted with an autofocus motor which the Sigma and Canon’s own EF 35mm f1.4L are.
When you add to this that Samyang’s 35mm lens fails to deliver anything like the sharpness and loses about 2/3 of a stop of transmission: it does not look like such a bargain. In build quality the Zeiss lenses have a great feel, using traditional materials in a way that is likely to mean they will retain their value well. The performance of the Zeiss lenses is very good but even the version at f2 is still more expensive than the better performing Sigma.
The score for resolution of the Sigma lens was 17.3 P-MPix making it one of the sharpest lenses available for the Canon EOS 5D Mk II. At f2.8 the lens performs almost consistently from corner to corner, but since an f1.4 lens is often bought to be used wide open it is impressive to see that thequality is maintained at a good level even for f1.4. Zeiss’s 35mm f2 scored 14.5 P-MPix and the Samyang 35mm F1.4 scored 11.5 P-MPix